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Spratt. — Some Observations on the 
attached at one side to the rest of the spore wall (PI. XXXII, Fig. 19). 
Another variation is caused by the contents germinating in situ in the 
portion of the spore wall (Fig. 19). 
The third type is exhibited in those cases in which the exospore and 
possibly also the endospore become mucilaginous (Fig. 30), and the proto- 
plast divides in its original position in the filament. 
These three types agree with those described by Fritsch for Anabaena 
sp., whilst the fourth is in accordance with Borzi’s observations. In this 
case the contents divide by a delicate wall into two initial cells of the fila- 
ment (Fig. 21, a). After this the membrane splits (Fig. 21, b), and then the 
cells can expand and continue their growth (Fig. 21, c). 
Formation of Gonidia. 
Reproductive bodies termed gonidia have long been known to occur 
in the Chamaesiphoneae, where they are well differentiated, and a number 
of observations suggest their formation in the Cyanophyceae. Brand 
describes their occurrence in Phormidium uncinatmn> where they arise 
singly by the rejuvenescence of the whole or greater part of the cell con- 
tents. He also observed the liberation of these bodies from the heterocysts 
of Nostoc sp., and adds that similar structures may be developed from the 
vegetative cells in these species. Fritsch found in some of his old material 
some rather abnormally shaped cells amongst heterocysts and sporogenous 
filaments, which he says had their contents rounded off and contracted, 
and they had acquired a new membrane of their own inside that of the 
mother-cell. He also observed the liberation of these contents as a spherical 
gonidium, but saw no indication of division either before or after, and 
concluded that they were caused by the arrest of spore formation. 
The formation of gonidia appears to play an important part in the life 
cycle of Anabaena Cycadeae , as was suggested above. It is interesting 
that it should be in this Alga, living in such a unique position, in symbiosis 
with a plant which has existed and flourished through a very long geological 
period, that we should have a confirmation of the phenomenon hitherto 
only observed by Brand, namely, the germination of the contents of the 
heterocysts for purposes of reproduction. This may be observed in material 
from old nodules and hanging-drop cultures, particularly in such as have 
been allowed to undergo partial desiccation, and then favourable conditions 
for further development have been restored. 
Material obtained in this way is composed mainly of heterocysts and 
spores. The former have a third investment inside, round the contracted 
cell contents (Fig. 22), which are no longer homogeneous, but have resumed 
their granular appearance. The contents undergo direct division, so that 
two small granular bodies are apparent in the newly-formed membrane 
(Fig. 23), each of which divides directly again, and eventually a number of 
